Cold-setting flexible polyurethane foams are normally used for the production of upholstery elements. Conventional cold foams are suitable for use as seating upholstery by virtue of their elasticity. By using special combinations of raw materials which are atypical of flexible foams, it is possible to produce cold-setting polyurethane foams which, in contrast to conventional cold foams, have advantageous insulating properties. These so-called "tired" foams (foams with slow recovery) are suitable for sound-proofing purposes and wherever good damping properties are required.
Open-celled polyurethane foams with a high flow resistance have the capacity to absorb airborne sound required of an acoustic material (see H. Schmidt: Schalltechnisches Worterbuch, Dusseldorf 1984). The capacity for absorption of airborne sound, which is due to external friction at the interfaces, is to a large extent determined by the cell structure and openness of the cells of a foam. In cold-setting flexible polyurethane foams these properties can be adjusted to a certain extent without any need to alter the basic raw materials, i.e., the polyol and the isocyanate. The open cell structure alone is not sufficient for absorption in the lower frequency range and, particularly for absorbing structure borne sound it is necessary for the structure of the flexible polyurethane foam itself to have a capacity for intensive damping.
The damping property, which is characterized by the loss factor, may be considerably improved in polyurethane foams, particularly by using special polyols and/or isocyanates. DE-AS 2,751,774, for example, describes a sound damping composite system which contains a flexible polyurethane foam as the spring in a mass-spring system. The flexible foam described in said specification has good damping properties which prevent coincidence break-in at a frequency range of from 150 to 10,000 Hz. The good damping is achieved by a combination of raw materials containing about 20% rigid foam polyol with a hydroxyl number of about 400 and 80% flexible foam polyol with a hydroxyl number of about 50. An additional insulating and damping effect is obtained by including heavy spar as inorganic filler.
DE-OS 3,313,624 describes a combination of raw materials in which the hydroxyl-containing component includes inter alia at least two different polyether polyols. One of these polyols must have an OH number of from 180 to 400 and must be present in the polyol mixture at a concentration of at least 15% by weight. Flexible polyurethane foams with moduli of elasticity of about 5.times.10.sup.5 N/m.sup.2 and loss factors of about 0.35 may be produced with such a combination.
It was an object of the present invention to find a combination of raw materials for the production of highly damping foams, i.e., foams which have a loss factor of at least 0.5 and preferably above 0.9. It was surprisingly found that this problem could be solved according to the invention, as described below.